1. Field of the Invention
This invention relates to an apparatus for cutting flat-rolled metal products such as metal plate, sheet and strip that makes cuts along the length of a moving flat-rolled metal product employing paired circular rotary knives.
2. Description of the Prior Art
Among the metal strip cutting apparatuses are rotary shears or side trimmers consisting of a pair of circular rotary knives that are disposed parallel to each other. Side trimmers are used to establish uniform strip width by continuously cutting off the edges of a strip throughout the entire length thereof, when the strip does not have a uniform width in an as-rolled state.
In actual operation, considerably large amounts of strip edge material, frequently exceeding twice the strip thickness, must be cut off because of instable variations in constraint, widthwise movement, flatness and other conditions of the strip. A big problem here is high percentages of scrap generation. On the other hand, the great progress in the shape control technology of strip rolling mills, which has been particularly remarkable in recent years, has made it possible to obtain uniform width throughout except in a few limited portions where broader strip width results from unusual rolling operations. Here arises the need to perform intermittent cutting operations to remove the excess width in such limited portions. However, the technologies to remove such desired amount from strip edges as is smaller than strip thickness (hereafter called extra-narrow-width cutting) and to intermittently remove localized excess width (hereafter called localized cutting) are still incomplete. The following problems will arise if an attempt is made to carry out the extra-narrow-width and localized cutting operations using a conventional side trimmer:
(a) Under a loose restraint, a strip tends to escape from the rotary knives when the cutting operation begins slipping thereover to create surface forces acting both widthwise and lengthwise. Particularly when the strip edges are rounded, the escape from the strip is so pronounced that the rotary knives cannot secure a good bite. Consequently, extra-narrow-width and localized cuttings are difficult to accomplish.
(b) If a strip is thoroughly restrained widthwise and the rotary knives are allowed to achieve a forcible bite, the strip tends to buckle and undergo resulting deformation. If extra-narrow-width cutting is performed under this condition, undesirable burrs will result and produce rough edges.
(c) The shape and flow of scrap are unstable so that the collection of scrap becomes difficult.
As such, conventional side trimmers are still widely used to continuously remove the unwanted width, which is larger than strip thickness, from both edges of a strip throughout the whole length thereof.